This commit includes a bunch of minor things:
- change keyboard shortcut to 'E' to not conflict with anything
- move `disabled` check from operation into action and simplify
- use `actionMoveNode` to place the detached node at the mouse cursor
- disable the operation if the node is connected to hidden features
- lots of code simplification
- make the icon more centered
Before: We drew 2 fontawesome comment icons, on on top of the other
After: Moved icon into iD spritesheet and gave it an actual `stroke` property that can be styled
Bryan Housel